Field of the Invention
Aspects of the present invention relate generally to wireless communications systems, and more particularly, to a method and communications apparatus for performing a cell reselection process in a wireless communications system.
Description of the Related Art
The term “wireless”, normally refers to an electrical or electronic operation, which is accomplished without the use of a “hard wired” connection. “Wireless communications”, is the transfer of information over a distance without the use of electrical conductors or wires. The distances involved may be short (a few meters for television remote controls) or very long (thousands or even millions of kilometers for radio communications). The best known example of wireless communications is the cellular telephone. Cellular telephones use radio waves to enable an operator to make phone calls to another party, from many locations world-wide. They can be used anywhere, as long as there is a cellular telephone site to house equipment that can transmit and receive signals, which are processed to transfer both voice and data to and from the cellular telephones.
There are various well-developed and well-defined cellular communications technologies. For example, the Global System for Mobile communications (GSM) is a well-defined and commonly used communications system, which uses time division multiple access (TDMA) technology, which is a multiplex access scheme for digital radio, to send voice, data, and signalling data (such as a dialed telephone number) between mobile phones and cell sites. The CDMA2000 is a hybrid mobile communications 2.5G/3G (generation) technology standard that uses code division multiple access (CDMA) technology. The UMTS (Universal Mobile Telecommunications System) is a 3G mobile communications system, which provides an enhanced range of multimedia services over the GSM system. The Wireless Fidelity (Wi-Fi) is a technology defined by the 802.11 engineering standard and can be used for home networks, mobile phones, video games, to provide a high-frequency wireless local area network. The LTE (Long Term Evolution) and the LTE-Advanced evolved from the LTE is a 4G mobile communications system, which provides high-speed data transmission over the 2G and 3G systems.
In general, if power to a communications apparatus is turned on, the communications apparatus searches the cells of a Public Land Mobile Network (PLMN), selects a cell, connects to a communication network of the selected cell, and adjusts a channel. If the communications apparatus camps on one or more cells in a power-on state, the communications apparatus searches for the cell which can provide a better signal than that of a serving cell and performs a cell reselection process.
The cell reselection process of the communications apparatus is a process of selecting a cell with better conditions than those of the serving cell based on a radio wave measurement or a priority-based reselection (PBR) algorithm of an idle state. The cell reselection process of the communications apparatus may allow the communications apparatus to reselect an ambient cell that satisfies the PBR algorithm among suitable cells.
That is, if the communications apparatus does not receive a service from a serving cell which exists currently, or if the communications apparatus discovers a better cell than a current serving cell, the communications apparatus performs a cell reselection process to a neighbor cell to maintain smooth service.
The cell reselection process is performed based on the PBR algorithm. In some situations, the communications apparatus performs an unnecessary cell reselection process. For example, the communications apparatus reselects from cell A to cell B, but immediately reselects to cell C. That is cell A→cell B→cell C. Cell B may be an intervening cell through which the communications apparatus passes to camp on cell C, which is the target cell. A cell reselection process to cell B may be unnecessary. The cause of this situation is that the communications apparatus may perform the cell reselection process according to signal strengths or signal quality when the communications apparatus does not receive a priority order defined by a network operator from the network, or the communications apparatus may perform the cell reselection process according to the priority order but the signal strength or the signal quality of the higher priority cell is very bad or an evaluation time of the higher priority cell is not satisfied. For this reason, there is a problem in that power consumption of the communications apparatus may occur due to the unnecessary cell reselection process.
Accordingly, in order to solve the problems, a communications apparatus and method for performing a cell reselection process is needed.